Multi-screen projector setting

ABSTRACT

A projection assembly comprising at least a first screen ( 14 ) and a second screen ( 10 ). The first screen ( 14 ) is at an angle with the second screen ( 10 ). The first screen ( 14 ) is adapted to reflect light projected onto it predominantly or exclusively in one or more angular ranges that do not intersect with the second screen ( 10 ). The invention also pertains to a method for projecting images with such a projection assembly, comprising projecting a first image with the first projector ( 16 B) on the first screen ( 14 ), and projecting a second image with the second projector ( 16 A) on the second screen ( 10 ).

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/901,915 filed Dec. 29, 2015, which is a national phase ofInternational Application No. PCT/EP2014/069429 filed Sep. 11, 2014 andpublished in the English language, which claims priority to GB 1316140.1filed Sep. 11, 2013 and GB 1403022.5 filed Feb. 20, 2014, which are allhereby incorporated herein by reference.

FIELD OF THE INVENTION

The present application relates to projection assemblies having aplurality of screens suitable for viewing a projected image, andoptionally one or more projectors appropriately arranged to project aprojected image onto these screens as well as to method of constructingand operating such assemblies, controllers and software for suchassemblies.

BACKGROUND OF THE INVENTION

In U.S. Pat. No. 5,964,064 “Theater with multiple screen threedimensional film projection system” a theater is disclosed including anaudience seating area, a stage and at least three projection screens.Right and left projection screens are positioned at an angle to thecenter projection screen. Multiple film projectors simultaneouslyproject a three dimensional film onto the three projection screens.Three dimensional film elements appear to move seamlessly from oneprojection screen to the next. In a live action show, actors, stage setsand show action equipment appear to interact with the three dimensionalfilm. The filmed set blends with the stage sets to give dimension and afeeling of depth to the viewing audience. The audience cannot easilydistinguish between the real elements and filmed elements therebyintensifying the theater experience.

In the proposed settings, the light reflected by e.g. the left screenwill reach not only the audience but also the center screen and theright screen. The same holds mutatis mutandis for the light reflected bythe center screen and the right screen. This usually causes visualartefacts that will impact the viewer experience negatively.

A similar problem exists for images projected on dome shaped screenwhere images can be projected by two or more projectors. In U.S. Pat.No. 6,909,543 “Foveated Display System”, an improved theater geometry isdisclosed which is capable of providing improved image resolution andimproved image contrast over prior systems. This is achieved with aunique projection geometry and image re-mapping technique. The projectedimage is provided with a continuously variable image resolution andbrightness over the surface of a preferably dome-shaped screen which isto receive the image, concentrating the resolution and the brightness ofthe image within the central field-of-view of viewers that areunidirectionally seated in the theater, and sacrificing resolution andbrightness toward the outside edges of the viewers' field-of-view. Theresult is a more efficient use of available projector resolution andbrightness, an increase in the number of quality seats available in thetheater, and an enhanced image contrast due to reductions in the lightwhich is scattering from image elements on the sides and to the rear ofthe screen.

If applied to a theater as described in U.S. Pat. No. 5,964,064,contrast and resolution would be highest on the central screen and woulddecrease on the lateral screens. The attention of the spectators beingdrawn from one screen to another as three-dimensional film elementsappear to move seamlessly from one projection screen to the next, thecentral field of view of viewers can move rapidly from one screen toanother. Without adaptation, the method proposed in U.S. Pat. No.6,909,543 will lead to situations where the spectators will experiencevariation in brightness not linked to the content of the images beingprojected, but to the screen on which they are projected.

U.S. Pat. No. 8,149,508 “System for providing an enhanced immersivedisplay environment” discloses an immersive dome including a number ofnovel features designed to enhance the performance of the immersive domeover other immersive dome environments. Projectors are mounted in amulti-tier tower, out of sight beneath a viewing platform positioned toprovide optimal wrap-around viewing. The projection surface consists ofopen-cell foam that allows passage of behind-surface sound into the domewhile allowing unwanted ambient noise within the dome to escape. Avisually-reflective coating, in conjunction with the open cellstructure, provides a textured surface that acts as a micro-baffle andsuppresses cross-reflection of projected imagery. The surface of thescreens is structured with a plurality of cavities defining verticalwalls that extend into the screen from the projection surface; whereinsaid plurality of cavities terminate before extending through thescreen, and wherein the plurality of cavities form micro-baffles; andwherein light at near normal incidence is reflected and wherein light atoblique angles of incidence is trapped and absorbed by said cavities forsuppressing visible cross-reflectance. Projection having to be doneperpendicularly to a screen, the proposed solution cannot be transposedto theater settings where one or more projectors cannot be placed so asto project perpendicularly to a screen without loss of luminosity andcreating visual artefacts.

As was the case with the other solutions described, the solutiondescribed in U.S. Pat. No. 8,149,508 will not be effective when thespectators are spread over a large area and away from a central positionor “sweet spot”.

Similar problems exists with the solution proposed in U.S. Pat. No.7,548,369 “Projection-receiving surface comprising a single sheet formedinto a plurality of catenoid-like mirrorlettes”, where the sweet spot isalong a perpendicular to each screen element. The field of view can betuned but is always centered on the normal to the screen elements.Therefore, the problem is not solved: increasing the field of view ispossible by decreasing the cut-off rate of the screens but then thecontrast of the image projected on one screen element is reduced by thelight reflected on other screen elements. Furthermore, the optical axisof the projector has to be aligned with the normal to the screen whichimposes restrictions to the position that the projectors can takerelatively to the screen on which they project.

In the system disclosed in U.S. Pat. No. 7,221,506, entitled “Method andsystem for projecting audio and video in an outdoor theater”, images areprojected onto two adjacent screens whereby one screen is movable withrespect to the second screen. A projection system disposed generally infront of the two screens is capable of displaying images on each screenindependently when the two screens are in an “open” position or on bothscreens together when the two screens are configured in a “closed”position. In a first “open” configuration, the images viewable on onescreen are not viewable to the viewers of images on an adjacent screenand, in a second “closed” configuration, images are displayed on bothscreens together (forming a single, planar viewing surface) so as to beviewable by all members of the audience. In addition, a berm isconfigured between the viewing area of one screen and the viewing areaof the other screen to create an audio and visual barrier between thetwo screens.

In the arrangement disclosed in JP 2008-175960, mirrors are installedbetween the projection devices and screens so that distances from theprojection devices to the screens may be the same as distances from theobserver seat to the screens, with a view to providing projection videowith which a feeling of presence is obtained without a sense ofincongruity as seen from an observer seat.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided aprojection assembly comprising at least a first screen and a secondscreen; wherein the first screen is at an angle with the second screen;and wherein the first screen is adapted to reflect light projected ontoit predominantly or exclusively in one or more angular ranges that donot intersect with the second screen.

The term “projection assembly” as used herein refers to a plurality ofscreens suitable for viewing a projected image, and optionally one ormore projectors appropriately arranged to project a projected image ontothese screens. The “projection assembly” may also be referred to as a“projection setting” or a “theater setting”.

The term “predominantly” is used herein to denote that a large part ofthe reflected light is situated in angular ranges that do not intersectwith the second screen. This large part is preferably at least 80% ofthe reflected light energy, more preferably at least 90% of thereflected light energy, even more preferably at least 95% of thereflected light energy, and most preferably at least 99% of thereflected light energy.

The term “at an angle” is used to indicate that the first screen and thesecond screen are not coplanar or parallel. In particular, it is used toindicate that the inner angle formed by the first screen and the secondscreen, on the side where a viewer is intended to be located, is lessthan 180°. In this geometry, light projected onto the first screen andreflected omnidirectionally by said first screen would reach the secondscreen, where it would result in a visual artifact. The presentinvention aims to avoid that phenomenon. The inner angle formed by thefirst screen and the second screen may, for example, be between 90°(e.g., following a corner of a rectangular viewing area) and 135° (e.g.,forming a first half of the transition in a corner of a rectangularviewing area, another screen at the same angle being required tocomplete the corner).

The described directionally selective light reflection by the firstscreen occurs when light is projected onto the first screen from theprojection direction corresponding to the desired theater setup.Optionally, the described directionally selective light reflection bythe first screen occurs regardless of the angle of incidence of thelight impinging on the first screen.

It is an advantage of the projection assembly according to the presentinvention that incident light arriving on the first screen will not bereflected onto the second screen, such that interference between theimage on the first screen and the image on the second screen can beavoided. Preferably, the non-interference relationship between thescreens is reciprocal, such that the second screen exhibits the sameproperty towards the first screen.

In an embodiment of the projection assembly according to the presentinvention, the first screen is a lenticular screen.

Lenticular screens can be manufactured in an economical way, andadvantageously provide the desired limitation of the angular range ofreflection.

In an embodiment of the projection assembly according to the presentinvention, the thickness of the first screen is not constant in at leastone direction across the screen.

By modulating the thickness of the screen, the screen will presentpartial surfaces having different orientations. These partial surfaceswill reflect incident light according to their respective orientations.Partial surfaces that have an orientation so as to reflect incidentlight towards the audience may be given better reflectivity properties(e.g., white coating) relative to partial surfaces that have anorientation so as to reflect incident light towards the second screen(which may for example be given a black coating). The amplitude of thethickness variations may vary according to the application between a fewtenths of millimeters to a few centimeters.

In an embodiment of the projection assembly according to the presentinvention, the thickness of the first screen varies in a sawtoothfashion in at least one direction across the screen.

It is an advantage of this embodiment that this is a geometricallysimple way to provide the partial surfaces discussed above, as thesawtooth naturally has two sets of sections having different respectiveorientations.

In an embodiment of the projection assembly according to the presentinvention, a first plurality of sections of said sawtooth pattern arerotated away from said second screen over an angle between 5° and 30°.

As will be explained in more detail below, the inventors have foundthat, surprisingly, a rotation angle of up to 30° reduces the reflectiontowards the second screen significantly without substantially impactingthe brightness of the image as seen by the audience.

In an embodiment of the projection assembly according to the presentinvention, a second plurality of sections of said sawtooth pattern arerotated towards said second screen, said second plurality of sectionshaving a surface with reduced reflectivity.

The “back sections” of the sawtooth pattern may be painted black, orotherwise given low reflectivity properties.

In an embodiment of the projection assembly according to the presentinvention, the thickness of the first screen varies periodically.

In an embodiment, the projection assembly according to the presentinvention further comprises a third screen arranged at an angle with thesecond screen. In a particular embodiment, the second screen is betweenthe first and third screens.

In an embodiment, the projection assembly according to the presentinvention further comprises a first projector arranged to project firstimages on the first screen and a second projector arranged to projectsecond images on the second screen.

In a specific embodiment, the projection assembly further comprisescontrol means configured to control the first projector in such a waythat the brightness of the image projected on the first screen is afunction of the brightness of the image projected on the second screen.

In a specific embodiment, the projection assembly further comprisescontrol means configured to control the first projector in such a waythat the brightness of at least a part of the image projected on thefirst screen is a function of the brightness of at least a part of theimage projected on the second screen.

In a specific embodiment, the projection assembly further comprisescontrol means configured to control the first projector in such a waythat the brightness of at least one pixel of the image projected on thefirst screen is a function of the brightness of at least one pixel ofthe image projected on the second screen.

In a specific embodiment, the projection assembly further comprisescontrol means configured to control the first projector in such a waythat the brightness of at least one pixel of the image projected on thefirst screen is a function of the brightness of a cluster of pixels ofthe image projected on the second screen, the cluster of pixels havingfewer pixels than the number of pixels projected on the second screen.

It is an advantage of this embodiment that the required amount ofcomputational power is decreased.

In a specific embodiment, the projection assembly further comprisescontrol means configured to control the first projector in such a waythat the brightness of at least one cluster of pixels of the imageprojected on the first screen is a function of the brightness of acluster of pixels of the image projected on the second screen, thecluster of pixels on the first screen having fewer pixels than thecluster of pixels projected on the second screen.

This embodiment will further decrease the required amount ofcomputations and complexity of the function to be evaluated to take thebrightness of images on the second screen into account.

According to an aspect of the present invention, there is provided amethod for projecting images with a projection assembly, the methodcomprising projecting a first image with the first projector on thefirst screen, and projecting a second image with the second projector onthe second screen. The projection assembly may be an assembly accordingto an embodiment of the first aspect of the present invention, asdescribed above, whereby the first screen reflects light projected ontoit by the first projector predominantly or exclusively in one or moreangular ranges that do not intersect with the second screen. The methodmay further include setting a first screen at an angle with a secondscreen so that the first screen reflects light projected onto it by thefirst projector predominantly or exclusively in one or more angularranges that do not intersect with the second screen.

In an embodiment, the method according to the present invention furthercomprises adjusting the brightness of the first image in function of thebrightness of the second image.

In an embodiment, the method according to the present invention furthercomprises adjusting the brightness of at least a part of the first imagein function of the brightness of at least a part of the second image.

In an embodiment, the method according to the present invention furthercomprises adjusting the brightness of at least one pixel of the firstimage in function of the brightness of at least one pixel of the secondimage.

In an embodiment, the method according to the present invention furthercomprises adjusting the brightness of at least one pixel of the firstimage in function of the brightness of a cluster of pixels of the secondimage, the cluster of pixels having fewer pixels than the number ofpixels in the second image.

In an embodiment, the method according to the present invention furthercomprises adjusting the brightness of at least one cluster of pixels ofthe first image in function of the brightness of a cluster of pixels ofthe second image, the cluster of pixels of the first image having fewerpixels than the number of pixels in the first image.

According to an aspect of the present invention, there is provided acontroller configured for use as the control means of embodiments of theprojection assembly according to the present invention and/or to performthe adjusting of embodiments of the method according to the presentinvention.

According to an aspect of the present invention, there is provided acomputer program product comprising code means configured to cause aprocessor to carry out the function of the control means of embodimentsof the projection assembly according to the present invention and/or toperform the adjusting of embodiments of the method according to thepresent invention.

The technical effects and advantages of the embodiments of the method,the controller, and the computer program product according to theinvention correspond mutatis mutandis to those of the correspondingembodiments of the projection assembly according to the invention.

BRIEF DESCRIPTION OF THE FIGURES

These and other features and advantages of embodiments of the presentinvention will now be described in more detail with reference to theaccompanying drawings, in which:

FIG. 1 illustrates a projection assembly according to an embodiment ofthe present invention;

FIG. 2a schematically illustrates the causes of ghost images in amultiple-screen projection setting;

FIG. 2b illustrates an exemplary scenery that could be sensitive togenerating artefacts in a multiple-screen projection setting;

FIG. 3 schematically represents projection and viewing angles in amulti-screen theater setting;

FIG. 4 schematically represents an example of simplified lenticules,formed by thickness variations of a screen;

FIG. 5 schematically represents an exemplary screen surface withlenticules;

FIG. 6 schematically represents an exemplary screen surface withlenticules, where groups of adjacent lenticules have the same slope;

FIG. 7 schematically represents an exemplary screen surface withlenticules having baffles attached to them;

FIG. 8 schematically represents an exemplary screen surface withlenticules, where groups of lenticules reflect light in three differentangular ranges;

FIG. 9 illustrates a method for structuring paint, wherein a nozzlesprays paint through a mesh placed between the nozzle and the screenbeing painted;

FIG. 10A shows a top view of exemplary lenticules;

FIG. 10B shows a section of the lenticules along the axis A-B indicatedon FIG. 10A;

FIG. 11A shows a top view of exemplary lenticules have a varying crosssection;

FIG. 11B shows a section of the lenticules along the axis A-B indicatedon FIG. 11A; and

FIG. 12 is a diagram of simulated light reflection in function of theangle of a sawtooth pattern on a screen surface (upper line: “towardsaudience”, lower line: “towards main screen”).

DETAILED DESCRIPTION OF EMBODIMENTS

A first embodiment of projector settings considered in this invention isas shown on FIG. 1. A theater 5 which has screens facing an audienceseating area 8 having seats 9, a center projection screen 10, a rightprojection screen 12, and a left projection screen 14. The right andleft projection screens (12, 14) are positioned at an angle to thecenter projection screen 10. In a typical setup, the angles between eachof the side screens 12, 14 and the center projection screen 10 areapproximately 90°, such that the projection zone can follow the contoursof one side of a substantially rectangular theater. Some of the seatscan be surrounded by the screens on three sides. The projection screenscan be flat or concave. Preferably, the screens are flat.

The screens can be jointed or not (i.e. with a gap between screens froma few millimeters to several meters or more). The gap between screenscan be filled with one or more objects (e.g. columns or pillars 18 and19) or empty.

In the back of the theater 5 are three projection rooms 20. In eachprojection room 20 are multiple film projectors 16A, 16B, 16C. As shownon FIG. 1, film projectors 16A project a portion of the film onto thecenter projection screen 10. Film projectors 16B project another portionof the film onto the left projection screen 14. Film projectors 16Cproject a third portion of the film onto the right projection screen 12.The projected images from the center projector 16A may abut or evenoverlap with the projected images from the side projectors 16B and 16C.In this manner, the film is presented to the audience in panorama. Thefilm elements may move seamlessly from one screen to the next, makingthe film more realistic.

With conventional screens, with diffusion characteristics close to aLambertian projection screens, some of the light projected by the sideprojector 16B on the left projection screen 14 will reach the centerprojection screen 10 (see FIG. 2A) and the right projection screen 12.Similarly, some of the light projected by the side projector 16C on theright projection screen 12 will reach the center projection screen 10and the left projection screen 14. This will create visual artefacts,i.e. the visual content projected on one of the screen by thecorresponding projector will appear to have been modified: the colorsand light intensity viewed in the audience on one of the screen will notbe those intended; the images can appear blurred and/or washed-out.

The amount of light that is reflected from one of the screens (“primaryscreen”) to another one of the screens (“secondary screen”) can beestimated, if certain assumptions are made about the screens. In thefollowing example, the screen surfaces are assumed Lambertian and thereare 90° angles between the main screen and each side screen.

The incident light on the primary screen, which can be considered asbeing equal to the luminous power F of the projector divided by theimage surface S, will be reflected in such a way that the luminance isthe same from all viewing directions. In the case of reflectivity of theLambertian type with unity gain, the luminance L can be determined infunction of F:

L=F/(πS)

where L is expressed in cd/m², F is expressed in lumen, and S isexpressed in m².

For a certain (small) white object with size dS projected on the primaryscreen, the luminous power F_(m) in an area dA on the secondary screen,caused by the incidence of reflected light on that secondary screen, isgiven by:

${d^{2}F_{m}} = {\frac{F}{\pi \; S}\frac{\cos \mspace{11mu} \theta \mspace{11mu} \cos \mspace{11mu} \phi}{r^{2}}{dSdA}}$

where the light is reflected from the primary screen to the secondaryscreen under an angle θ from the normal of the primary screen, andarrives at the secondary screen under an angle φ from the normal of thesecondary screen.

In a set-up with perpendicular screens, if a is the distance from theprojected area away from the corner, and b is the distance on thesecondary screen away from their intersect corner, you can derive thatthe illumination on the main screen is proportional to:

$F_{m} \propto \frac{ba}{\left( {b^{2} + a^{2}} \right)^{2}}$

This means the illumination by the primary screen onto the secondaryscreen will be at its highest in an area not so far from the cornerarea. If the secondary screen is also a Lambertian screen, thereflection towards the audience will also be highest in this area closeto the corner.

While the reflection of the image projected onto the primary screentowards the secondary screen does not produce a specular image on thelatter, it is clear from the above that the main effect of thereflection will occur in a gradually delimited area of the secondaryscreen.

The most disturbing artefacts happen when there is a large difference inthe brightness of images projected on at least two of the screens. Iffor instance, the image projected on the central screen is mainly dark(e.g. a night sky; see FIG. 2B) and the image projected on one of thelateral screen contains one or more bright areas 21 (e.g. a full moon;see FIG. 2B), the reflection 22 of those bright areas on the centralscreen will appear as a “ghost” or “glare”.

By using a lateral screen 14 that reflects light in one or more favoredangular ranges that do not intersect with the center screen 10 or withthe right screen 12, the visual artefacts discussed here above arecanceled or at the very least reduced.

By using lateral screens 12 and 14 that substantively reflect lightprojected on them respectively by projectors 16C and 16B in one or moreangular ranges that do not intersect with the central screen 10 and theopposite lateral screen (respectively 14 and 12), the present inventionallows viewers in the audience to perceive the lateral screens insubstantially the same way regardless of their position in the seatingarea 8, increases the overall efficiency of the projection setting bydirecting the light reflected by the lateral screens preferentially inthe direction of the audience, and reduces or cancels visual artefactscaused by light spill-over from one screen to the other.

The invention solves the problem of a projection setting comprising atleast a first screen and a second screen and where the first screen isat an angle with the second screen; by using a first screen thatreflects light in one or more angular ranges that do not intersect withthe second screen.

The first screen can be a lenticular screen where the geometry of thelenticules is such that hardly any light projected on the first screenwill be reflected on the second screen.

More generally, a suitable first screen has a thickness that is notconstant in at least one direction across the screen. The thicknessvariations are at least commensurate with the wavelength of the lightprojected on the screen. The thickness of the screen can be measuredfrom a reference surface e.g. the back of the projection screen. Thesurface of reference can be considered as a general surface of thescreen, the surface obtained when the surface structure like thelenticules have been smoothed out.

In particular, the thickness variations give the surface of the firstscreen a serrated appearance i.e. a section of the screen by a planeperpendicular to the general surface of the screen will look like ajagged, triangular waveform as seen on e.g. FIG. 4.

In particular, the thickness variations of the first screen repeat atregular spatial intervals in at least one direction on the screen. Ashere above, the periodicity of the thickness variations can be evaluatedon a perpendicular section of the screen. The resulting pattern may havethe appearance of a sawtooth.

The invention concerns not only projection settings where a singleprojector projects images on the first and second screen, but alsoprojection settings where a first projector projects images on the firstscreen and a second projector projects images on the second screen.

More generally, the invention applies to projection settings where Mprojectors project images on N screens (M and N being natural numbers).

In particular, there may be three screens on which images are projectedby one, two or three projectors.

An exemplary embodiment is now described in further detail withreference to FIGS. 1 and 2A. A first projector is positioned in front ofthe center screen as in commonplace theaters, e.g. at the back of thetheater, behind and above the spectators. A second projector ispositioned as in FIG. 1 or alternatively in front of the right screenand below (or above) the left screen. A third projector is positioned asin FIG. 1 or alternatively in front of the left screen and below (orabove) the right screen. The right and left screens are directionalscreens. By directional screens we mean screens that will reflect lightin preferred light cones or angular ranges, as described above. Thoseangular ranges may differ substantially from the angular range expectedfrom usual isotropic projection screens.

The directional screens can be lenticular screens as described in e.g.U.S. Pat. No. 1,279,262 “Projection screen” and U.S. Pat. No. 4,338,165“Method of making a high-gain projection screen”. The lenticules aredesigned so as to reflect the light in a favored angular range thatexcludes the opposite screen (i.e. the right or left screen) and thecenter screen. That is accomplished by forming the lenticules with anabnormally small vertical or horizontal curvature within the angularrange to be favored. That reduced curvature automatically increases thelinear dimension of the lenticule portion that corresponds to eachangular increment of the beam. An increased proportion of the availablelight is thereby concentrated into the favored beam sector. Thelenticule curvature is then progressively increased, typicallythroughout the remainder of the lenticule surface, at a rate sufficientto spread the reflected beam over the entire viewing area. The overallresult is represented on FIG. 3 for the left screen only. In a secondpreferred embodiment, the center screen is a lenticular screen with afavored angular range excluding at least part of the left and rightscreens.

In some cases it may be desirable to simplify the shape and themanufacturing of the lenticules. In general, the simplified lenticulesare obtained by varying the thickness of the projection screen. As seenon FIG. 2B, a suitable first screen may have a thickness that is notconstant in at least one direction across the screen. The zoomed-incartouche on FIG. 2B shows a perpendicular cross section of the leftscreen 14. The plane of the section is in this case a horizontal planeand the screens are substantially vertical. The thickness variations areat least commensurate with the wavelength of the light projected on thescreen. The thickness of the screen can be measured from a referencesurface e.g. the back of the projection screen. The surface of referencecan be considered as a general surface of the screen or in other wordsthe surface obtained when the surface structure like the lenticules havebeen smoothed out.

A first example of simplified lenticules is represented on FIG. 4. FIG.4 shows a section of a portion of screen 40. Screens being usually heldvertically, the section is in a plane perpendicular to the localvertical. The lenticules appear as serrations on the screen. Theserrations are on the side of the screen on which a projector projectslight. The lenticules 41, 42, 43, 44 and 45 are plane and at an anglewith the plane 46 of the screen 40. The size of a lenticule and/or theangle it makes with the plane of the screen may vary from lenticule tolenticule. For instance, on FIG. 4, the angle between the lenticule 41and the plane of the screen is α₁.

Embodiments of the invention are based on the insight of the inventorsthat a judicious choice of the angle of the sawtooth pattern yields avery efficient reduction of the undesired reflections, while maintainingvery good brightness of the desired image. If a sawtooth pattern is usedon the primary screen with white (reflective) segments aimed at theaudience and black segments aimed at the secondary screen, there is, atsufficiently small rotation angles α₁ (this is the angle of thereflective portion of the sawtooth relative to the main surface of thescreen), only a small effect on the luminance of that screen as seen bythe audience. The luminance only starts to decrease if the sawtoothangle becomes so big that the individual protrusions obstruct some ofthe white illuminated areas on the screen.

This can be explained using the assumptions introduced in themathematical derivation above. For the reflection to the secondaryscreen, the formula above will change to:

$F_{m} \propto \frac{\left( {{b\mspace{11mu} \sin \mspace{11mu} \alpha_{1}} - {a\mspace{11mu} \cos \mspace{11mu} \alpha_{1}}} \right)a}{\left( {b^{2} + a^{2}} \right)^{2}}$

For any light coming from the secondary screen and hitting the primaryscreen, it is obvious that the reflection is reduced by the sawtoothbecause already a large part of the light from this direction will hitthe black part of the sawtooth.

A simulation of the total amount of light directed towards the audienceand the light directed towards the secondary screen for an illuminationof a complete primary screen in this set-up, in function of the sawtoothangle, is shown in FIG. 12. The diagram shows that the reflectionstowards the secondary screen steeply decrease with an increasing angleof the sawtooth pattern, while the light reflected to the audienceremains substantially constant over the entire angular range from 0° to30°. Based on this analysis, the inventors have arrived at thesurprising result that a sawtooth pattern with an angle α₁ of up to 30°is highly preferred.

In particular, in another embodiment, on a lateral screen the anglebetween a lenticule and the plane of the screen on which the lenticuleis formed decreases as the distance between the lenticule and thecentral screen increases. This is illustrated on FIG. 5. Note that thedimensions of the lenticules may have been exaggerated on FIG. 5.Lenticule 55 is closer to the central screen than lenticule 54 etc. Theangle that lenticule 55 makes with the plane 56 of the screen 50 islarger than the angle that lenticule 54 makes with the plane 56 of thescreen 50. If a side of a lenticule is likely to reflect light in thedirection of another screen of the projection settings, that side may becovered with an antireflection coating 56 like e.g. black paint.

In another embodiment depicted on FIG. 6, the angle that lenticules onscreen 60 make with the plane 66 of the screen 60 will be the same for agroup of adjacent lenticules (e.g. lenticules 65, 64 and 63) and willdecrease to a common value for the following group of lenticules (e.g.62 and 61) on screen 60.

In another embodiment, baffles 76 affixed to at least some of thelenticules will reduce the impact of stray light reflected or receivedby the screen 70. In FIG. 7, an example of positioning for the baffles76 is given. The baffle 76 may be made of a light absorbing material orcoated with a light absorbing paint on both of their sides. In thatcase, the baffle 76 will bring the benefit of the antireflection coating56.

In another embodiment, the lenticules realize a periodic structure onthe screen. This periodic structure is meant to reflect the imageprojected in two or more favored angular ranges. Lenticules are groupedby K where K is the number of favored angular ranges within which thelight projected on the screen must be reflected. The groups are repeatedon the screen with a periodicity of K lenticules.

FIG. 8 shows a section of a screen where K is taken equal to three.Lenticules 81, 82 and 83 form a first group of lenticules that reflectlight in three different favored angular ranges. Lenticules 84, 85 and86 form a second group of lenticules that reflect the light in the samethree favored angular ranges. Lenticules 81 and 84 are identical as arelenticules 82 and 85 and 83 and 86 respectively. The group of lenticulesis repeated from one end of the screen 80 to another. A screen whosesurface would coincide with the general surface 86 of the screen 80would reflect light differently than screen 80. The period P of thelenticules is advantageously kept at the same order of magnitude as thesize of a pixel on the screen. The period P of the lenticules isadvantageously taken equal or smaller than the size of a pixel on thescreen. In particular, the period P and the size SP of a pixel on thescreen are advantageously so that R×P≈SP where R is a natural number.

The lenticules proposed in those embodiments can be engraved in thescreen 50. This is particularly the case for a screen 50 made of one ormore panels of hardened polymer like e.g. an acrylic resin. Thetechniques for engraving are similar to those relied on to engraveFresnel lenses.

The lenticules can also be formed by deposition of a thin film of resinon a screen 50; followed by a molding step where a negative mold ispressed on the deposited resin.

Examples of techniques to realize fine structures by molding are givenin e.g. US 2010/0226022 “Fresnel lens, the apparatus and the method ofmanufacturing thereof”.

Structuring the paint spread over a screen is another technique torealize lenticules of varied shapes and forms. The technique can beapplied to a wide range of existing walls, making it desirable forretrofitting existing projection settings like theaters and turning theminto multi-screen projection settings. The paint can be structured byinkjet printing.

In a first method, the nozzle of the printer is smaller than the smallerfeature required in the structured paint layer. The longer the nozzlewill spray paint on the same spot, the thicker the layer of paint onthat spot. By modulating the speed at which the nozzle is scanned acrossa screen, it is possible to realize different profile for thelenticules. In a first approximation, the slower the nozzle will scan afirst area of the screen, the thicker the layer of paint will be on thatarea. Conversely, the faster the nozzle will scan a second area of thescreen, the thinner the layer of paint will be on that second area.

In a second method for structuring paint, the nozzle 90 will spray paint91 through a mesh 92 placed between the nozzle and the screen 93 beingpainted as exemplified on FIG. 9.

The structured paint layer so obtained is best realized with a lightabsorbing material like black paint. This will help alleviate the glareproblem mentioned earlier. The regions of the lenticules that mustreflect the light in one or more preferred directions are coated with alight reflective coating. The reflecting coating may for instance be abright paint and in particular a white paint.

The reflective coating can be deposited with one of the two methodsdescribed here above.

To avoid visual artifacts on the screen like e.g. visible stripes, thefeature size (e.g. the distance between two lenticules on FIG. 4) shouldbe smaller than the size of the pixels projected on the screen.

The base structure drawn above is best formed using light absorbingmaterial like e.g. dark paint.

An alternative to the lenticules discussed so far are e.g. holographicstructures.

The complexity of the lenticules can be increased. For instance,lenticules with a hexagonal section can be used.

FIG. 10A shows a top view of the lenticules and FIG. 10B shows a sectionof the lenticules along the axis A-B on FIG. 10A. The inner walls of alenticule can be coated with different coatings, depending on theorientation of the wall. For instance, the walls meant to reflect lighttowards the audience are coated with a reflective coating 106 while thewalls most susceptible to receive light from another screen are coatedwith a light absorbing material 107.

Some of the area of the bottom of the lenticules can be coated with thereflective coating 106.

The coatings can be a function of the position of the lenticules on ascreen and in particular a function of the distance of a lenticules toanother screen, in particular the central screen. This is illustrated onFIG. 10B with lenticule 105 is closer to e.g. the central screen thanlenticule 101.

In a preferred embodiment, the light absorbing coating is coated on theinner walls of the lenticules that are not visible from a point chosenin the audience (e.g. point P on FIG. 1). The light reflecting coatingis applied to the inner walls of the lenticules that are visible fromthe point P in the audience.

In another preferred embodiment, the light absorbing or antireflectioncoating is coated on the inner walls of the lenticules that are notvisible from a projector e.g. the antireflection coating will be appliedto the inner walls of the lenticules on the left projection screen 14that are not visible from the projector 16B (e.g. the center of theprojection lens of projector 16B). The reflective coating will beapplied to the inner walls of the lenticules on the left projectionscreen 14 that are visible from the projector 16B. The reflective andanti-reflective coatings are then similarly applied mutatis mutandis onthe inner walls of the lenticules on the right projection screen 12.

A coating can be selectively sprayed on the inner walls of thelenticules by spray painting at an angle, with or without using a grid.

The lenticules on FIG. 10 have a constant hexagonal cross section i.e.the inner walls are perpendicular to the same surface e.g. the generalsurface of the screen. To avoid restricting the favored angular rangewithin which the screen will reflect the light of the projector toomuch, the inner walls may be made more diffusive. For instance, thesurface of the inner walls is roughened by any practical methods (e.g.by adjusting the viscosity of the paint that is spray painted at anangle on the inner walls of the lenticules).

In another preferred embodiment, the lenticules have a varying crosssection. The cross section at the base of the lenticules has a smallerarea than the cross section at the top of the lenticules. An example ofsuch lenticules is given on FIG. 11A/B.

The techniques discussed here above will cancel or at least reduce theglare caused by reflection of bright areas on a first screen to a secondscreen and in particular dark areas of a second screen.

If the glare is not reduced adequately by the techniques proposed hereabove, it can be further reduced by modulating the brightness of theimages projected on a first screen in function of the brightness of theimages projected on a second screen.

The brightness of a pixel on the first screen is the sum of two maincomponents. The first component is determined by the light projected onthe first screen by the projector aimed at that first screen. The secondcomponent is determined by the light reflected on the second screen andimpinging on the first screen at the position of the pixel beingconsidered.

A technique is hereby proposed to reduce the glare from a second screenon a first screen.

For any given pixel P on the first screen that must display a targetbrightness TB, the contribution CG of the glare to pixel P from all thepixels of the second screen is evaluated.

The pixels projected on the first screen are projected with a correctedbrightness CB=TB−CG. The resulting brightness of the pixels on the firstscreen will then be equal to CB+CG=TB−CG+CG=TB and the glare is reduced.It is immediately clear from the formula, that this technique can onlybe applied to pixels whose target brightness TB is sufficiently high toallow subtraction of the correction value CG. Thus, this method will notbe effective when glare is to be removed from an image which is intendedto be mostly dark.

The necessary calculations can be performed by a control means, whichmay be implemented as a dedicated hardware device, configurable hardwarelogic such as an FPGA, or an appropriately programmed microcontroller ormicroprocessor. This control means may be a controller incorporated intoa projector, and configured to control the brightness of the projectorbased on the outcome of these calculations. The control means may alsobe provided as a separate controller module. A computer readable mediumstoring a program that, when executed, causes a processor to carry outthe functions of the control means, and the program or software itself,are also embodiments of the present invention.

To perform the necessary calculations, the control means must haveaccess to the respective CG terms. The control means may receive a copyof the image signal of the second projector via a data communicationinterface, and apply a pre-programmed model of the glare distribution tothis image signal to determine the relevant CG terms for the variouspixels.

To reduce the complexity of the calculations, a coarser approach ispossible. The second contribution CG is not computed for every pixel onthe first screen but e.g. for a group of pixels (e.g. a square of 100pixels by 100 pixels). The complexity can further be reduced bycalculating the contribution CG based on an average brightness ofclusters of pixels on the second screen and evaluating the contributionto the glare of all these clusters to the clusters of pixels on thefirst screen. The clusters of pixels have fewer pixels than the completeimages projected on the respective screens.

Even with the above simplifications, the number of computations requiredto apply the glare cancelling technique may be prohibitive for areal-time implementation on a given hardware platform. In a variant ofthe technique, the necessary calculations are performed in advance, andcorrection information is encoded as metadata in the video stream thatis supplied to the projectors. This correction information may pertainto the entire video program, or it may be limited to any number ofspecific occurrences of bright images that are expected or known tocause disturbing visual artefacts if they are not corrected for.

While the invention is susceptible to various modifications andalternative forms, specific examples will be shown in the drawings anddescribed in detail. It should be understood, however, that theinvention is not limited to the particular forms or methods disclosed.Rather, the invention is intended to cover all modifications,equivalents and alternatives falling within the scope of the claims.

1. A projection assembly comprising at least a first screen and a second screen; said first screen and said second screen being flat; wherein the first screen is at an angle with the second screen; and wherein the first screen is adapted to reflect light projected onto it predominantly or exclusively in one or more angular ranges that do not intersect with the second screen.
 2. A projection assembly according to claim 1, wherein the first screen is a lenticular screen.
 3. A projection assembly according to claim 1, wherein the thickness of the first screen is not constant in at least one direction across the screen.
 4. A projection assembly according to claim 3, wherein the thickness of the first screen varies in a sawtooth fashion in at least one direction across the screen.
 5. A projection assembly according to claim 4, wherein a second plurality of sections of said sawtooth pattern are rotated towards said second screen, said second plurality of sections having a surface with reduced reflectivity.
 6. A projection assembly according to claim 3, wherein the thickness of the first screen varies periodically.
 7. A projection assembly comprising at least a first screen and a second screen; wherein the first screen is at an angle with the second screen; and wherein the first screen is adapted to reflect light projected onto it predominantly or exclusively in one or more angular ranges that do not intersect with the second screen; the projection assembly further comprising: a first projector arranged to project first images on the first screen and a second projector arranged to project second images on the second screen; and control means configured to control the first projector in such a way that the brightness of the image projected on the first screen is a function of the brightness of the image projected on the second screen.
 8. A projection assembly according to claim 7, wherein the control means is configured to control the first projector in such a way that the brightness of at least a part of the image projected on the first screen is a function of the brightness of at least a part of the image projected on the second screen.
 9. A projection assembly according to claim 7, wherein the control means is configured to control the first projector in such a way that the brightness of at least one pixel of the image projected on the first screen is a function of the brightness of at least one pixel of the image projected on the second screen.
 10. A projection assembly according to claim 7, wherein the control means is configured to control the first projector in such a way that the brightness of at least one pixel of the image projected on the first screen is a function of the brightness of a cluster of pixels of the image projected on the second screen, the cluster of pixels having fewer pixels than the number of pixels projected on the second screen.
 11. A projection assembly according to claim 7, wherein the control means is configured to control the first projector in such a way that the brightness of at least one cluster of pixels of the image projected on the first screen is a function of the brightness of a cluster of pixels of the image projected on the second screen, the cluster of pixels on the first screen having fewer pixels than the number of pixels projected on the first screen.
 12. A projection assembly according to claim 7, wherein the control means is configured to receive a copy of the image signal of the second projector via a data communication interface, and to apply a pre-programmed model of a glare distribution to said image signal in order to determine a contribution of the image projected on the second screen to the glare at each pixel of the image projected on the first screen.
 13. A method for projecting images with a projection assembly according to claim 7, the method comprising projecting a first image with the first projector on the first screen, and projecting a second image with the second projector on the second screen, and adjusting the brightness of the first image in function of the brightness of the second image.
 14. The method according to claim 13, further comprising adjusting the brightness of at least a part of the first image in function of the brightness of at least a part of the second image.
 15. The method according to claim 13, further comprising adjusting the brightness of at least one pixel of the first image in function of the brightness of at least one pixel of the second image.
 16. The method according to claim 13, further comprising adjusting the brightness of at least one pixel of the first image in function of the brightness of a cluster of pixels of the second image, the cluster of pixels having fewer pixels than the number of pixels in the second image.
 17. The method according to claim 13, further comprising adjusting the brightness of at least one cluster of pixels of the first image in function of the brightness of a cluster of pixels of the second image, the cluster of pixels of the first image having fewer pixels than the number of pixels in the first image.
 18. The method according to claim 13, further comprising applying a pre-programmed model of a glare distribution to an image signal of the second projector in order to determine a contribution of the image projected on the second screen to the glare at each pixel of the image projected on the first screen.
 19. A controller configured for use as the control means of claim
 7. 20. A computer program product comprising code means configured to cause a processor to carry out the function of the control means of claim
 7. 